10/23/2014

Diode IV Curve Experiment LabVIEW Graphical Representations

Andrew Powers, Hubert Walkowski, Cole Leether WENTWORTH INSTITUTE OF TECHNOLOGY

Abstract:

A LabVIEW simulation was run in order to see how an electrical signal

flowed to four different LED lights. A bread board circuit was set up and using

LabVIEW as a function control and also graphical output simulator, voltage was

run through the system. Once the system reached a certain current, the LEDs

would start to glow. Once they glowed completely, depending on the inputs on

the LabVIEW interface, graphical outputs of diode IV characteristics and change in

voltage with respect to current were gathered. From this lab, it is now known that

each of the four LED lights showed similar trends of blue, yellow, green, and red

IV characteristics, where blue took the most voltage to turn on at 2.47 bolts, then

green at 1.7 volts, and green and red turned on at 1 volt. Also, the red LED has the

highest voltage with respect to current. This all shows that the red LED takes the

longest to turn on.

Synopsis:

When lighting an LED, each color has a particular IV characteristic. Because

of this, voltage and current of each color LED differ. By using LabVIEW, it visually

shows the characteristics of each color LED with the IV characteristic graphs. Also,

voltage versus current graphs were created by LabVIEW to show the rate of

voltage change with respect to the current through the system. With both of

these graphical outputs, the voltage it takes to turn on each color LED was

understood.

Apparatus:

The electrical components used to construct the circuit consisted of a

power source, a voltage output reader, various colored diodes, a 1k resistor, a

bread board and the required test leads to connect the components into a circuit.

The below image expresses the complete set up of all the above listed

electrical components. The only aspect of the test equipment left out is the

computer in which LabVIEW was projected on giving us the various diode IV

curves as expressed in the below graphs.

The below figure explains the orientation of the resistor and diode in the

circuit used to run the testing for the diode IV curves.

(Vd)

Results:

Equations

I =𝑉𝑑 − 𝑉𝐷𝑀𝑀

𝑅

R = resistor (1000 ohms)

I = current

Vd = alternating supplied voltage

VDMM = voltage read from the DMM reading

The LabVIEW block diagram

IV characteristics

Red IV

Green IV

Yellow IV

Blue IV

dV/dI

Red dV/dI

Green dV/dI

Yellow dV/dI

Blue dV/dI

Discussion of Graphical Results:

Red Diode – On the IV curve, the current did not change significantly until the voltage reading reached 1.45 Volts. After this point, the curve became steeper due to the current increasing at a higher rate than the voltage reading. The slope of this IV graph changes slower than the rest of the graphs. This is shown by the curve on the dV/dI graph for the red diode, which decreases slope and eventually becomes horizontal, indicating a larger change in current compared to voltage.

Green Diode – On the IV curve, the current did not change significantly until the voltage reading reached 1.7 Volts. After this point, the curve’s steepness increases exponentially due to the current increasing at a significantly higher rate than the voltage reading. The IV graph for this diode has a slope that increases quicker than that of the red diode. This is shown by the curve on the dV/dI graph for the green diode, which has a large decrease in slope as voltage increases, and eventually becomes horizontal, indicating the higher change in current compared to voltage.

Yellow Diode – Similar to the green diode’s IV curve, the current did not change significantly until the voltage reading reached 1.7 Volts. After this point, the curve became steeper due to the current increasing at a significantly higher rate than the voltage reading. The slope of the yellow diode’s IV curve increased faster than that of the green diode. The relationship between the change in voltage and current is shown by the curve on the dV/dI graph, which decreases slope and eventually becomes horizontal, again, indicating that the current changes at a higher rate than that of voltage.

Blue Diode – On the IV curve, the current did not change significantly until the voltage reading reached 2.4 Volts. After this point, the curve became steeper due to the current increasing at a higher rate than the voltage reading. The slope of this graph increases faster than that of the red diode IV curve, but not as fast as the IV graph of the green diode. This is shown by the curve on the dV/dI graph for this diode, which decreases slope and eventually becomes horizontal, indicating a higher rate of change in current than voltage.

Conclusions:

All of the IV curves showed the same trend in that a specific amount of

voltage was required to turn on the specific diodes. The red diode activated at

1.45 volts, the green diode at 1.7 volts, yellow diode was 1.75 volts and the blue

diode activated at 2.4 volts. These voltages relate to the below table which

expresses the voltage drops for various colored diodes. The exact voltage values

do not measure up perfectly, but the experimental trend matches the theoretical

trend expressed in the below table. The red diode required the least voltage, then

green, yellow, and finally the blue diode required the highest voltage to turn on.

All of the IV slopes exponentially increased. The rate in which current increased

ranging from lowest to the highest was the red, blue, green and yellow diode

according to the graphs.

The second set of graphs are the rates of change of voltage over current.

The rate of change in current is greater than the rate of change of the voltage

resulting in the exponential downwards slope, and eventual leveling, of the

graphs.

In the end our data concluded that voltage does drop across a

diode/resistor electrical circuit.

Conventional LEDs are made from a variety of inorganic semiconductor materials. The

following table shows the available colors with wavelength range, voltage drop and material:

Color Wavelength

[nm]

Voltage drop

[ΔV] Semiconductor material

Infrared λ > 760 ΔV < 1.63 Gallium arsenide (GaAs)

Aluminium gallium arsenide (AlGaAs)

Red 610 < λ < 760 1.63 < ΔV <

2.03

Aluminium gallium arsenide (AlGaAs)

Gallium arsenide phosphide (GaAsP)

Aluminium gallium indium phosphide (AlGaInP)

Gallium(III) phosphide (GaP)

Orange 590 < λ < 610 2.03 < ΔV <

2.10

Gallium arsenide phosphide (GaAsP)

Aluminium gallium indium phosphide (AlGaInP)

Gallium(III) phosphide (GaP)

Yellow 570 < λ < 590

2.10 < ΔV <

2.18

Gallium arsenide phosphide (GaAsP)

Aluminium gallium indium phosphide (AlGaInP)

Gallium(III) phosphide (GaP)

Green 500 < λ < 570 1.9[70] < ΔV <

4.0

Traditional green: Gallium(III) phosphide (GaP)

Aluminium gallium indium phosphide (AlGaInP)

Aluminium gallium phosphide (AlGaP)

Pure green: Indium gallium nitride (InGaN) / Gallium(III)

nitride (GaN)

Blue 450 < λ < 500 2.48 < ΔV <

3.7

Zinc selenide (ZnSe)

Indium gallium nitride (InGaN)

Silicon carbide (SiC) as substrate

Silicon (Si) as substrate—under development

Violet 400 < λ < 450 2.76 < ΔV <

4.0 Indium gallium nitride (InGaN)

Purple Multiple types 2.48 < ΔV <

3.7

Dual blue/red LEDs,

blue with red phosphor,

or white with purple plastic

Ultraviolet λ < 400 3.1 < ΔV < 4.4

Diamond (235 nm)[71]

Boron nitride (215 nm)[72][73]

Aluminium nitride (AlN) (210 nm)[74]

Aluminium gallium nitride (AlGaN)

Aluminium gallium indium nitride (AlGaInN)—

down to 210 nm[75]

Pink Multiple types ΔV ~ 3.3[76]

Blue with one or two phosphor layers:

yellow with red, orange or pink phosphor added

afterwards,

or white phosphors with pink pigment or dye

over top.[77]

White Broad spectrum ΔV = 3.5 Blue/UV diode with yellow phosphor